textproduct: Rapid City

KEY MESSAGES

-Another lobe of tropical moisture expected Sunday into Monday, supporting more chances for rain

-Cool Sunday, especially on the SD Plains

-Seasonal and dry after Monday

UPDATE

Issued at 1032 PM MDT Sat Sep 26 2026

Recent CAMs and 00z NAM suggest a few showers could develop over northwestern SD overnight, though confidence too low to include any mentions in grids. Patchy fog has begun to develop over south central SD, this fog should continue to develop over portions of south central SD through late tonight into tomorrow morning as moisture continues to stream into the region. Made no major changes to the forecast aside from some minor tweaks to PoPs for tomorrow. Still expecting mostly cloudy skies and isolated to scattered showers across western SD tomorrow afternoon with chances for showers and storms increasing in the evening hours as warm front lifts through the area.

DISCUSSION

(This Afternoon Through Friday) Issued at 1059 AM MDT Sat Sep 26 2026

Upper trough will remain in place through early next week over the western CONUS, supporting mainly WSW flow aloft. Pattern change expected toward next weekend as a strong NE Pac upper trough dives into the Pac NW and supports a couple stronger upper troughs and associated sfc low's across southern Canada and the northern CONUS, flattening the flow aloft. Sfc trough has pushed through most of the FA. A period of breezy winds can be expected into the afternoon, esp in the lee of the Black Hills. Not much if any cool air with this front, just a drier airmass. Upper trough will drop into the SW CONUS Sunday and direct tropical moisture NE across the Rockies. Meanwhile low level SE return flow will develop, pushing LL moisture back west into the region. This will support much cooler conds on the SD Plains for Sunday, esp along the east slopes of the BH where moist upslope flow will be in place. Expect mostly cloudy skies there with light showers or drizzle possible. Isolated light rain showers will also be possible across the remainder of the SD Plains as pos theta-e adv will be ongoing through the day. Main lobe of deep moisture will arrive in the evening via a lead impulse, supporting a good chance of showers and isolated TS. Another window of higher chances of showers and storms can be expected Monday afternoon as the sfc trough moves through the area, with a few stronger storms possible on the SD Plains. Things dry out after Monday with seasonal temps expected into the upper 60s to low 70s the rest of the week, lows in the 40s/50s. Models are still indicating a stronger cold front next weekend, which could bring some frost as the upper trough over the NE Pac shifts east and forces cold air south out of Canada. However, the degree of CAA with this system still varies substantially among the various forecast models and ensembles, with temperature spreads really large.

AVIATION

(For the 06Z TAFS Through 06Z Sunday Night) Issued At 1056 PM MDT Sat Sep 26 2026

Patchy fog and low clouds will redevelop early Sunday morning across western SD. CIGS will be MVFR, perhaps IFR, but VSBY is expected to drop to IFR or lower (< 1 SM) due to patchy fog across some locations over the western SD plains. VFR conditions will continue through NE WY. Isolated showers are possible Sunday, but scattered showers and isolated thunderstorms will be possible Sunday evening as a system moves across the region.

UNR WATCHES/WARNINGS/ADVISORIES

SD...None. WY...None.